Behavior of Neural Cells Post Manufacturing and After Prolonged Encapsulation within Conductive Graphene-Laden Alginate Microfibers

Hydrodynamic Assembly of Astrocyte Cells in Conductive Hollow Microfibers

The manufacturing of 3D cell scaffoldings provides advantages for modeling diseases and injuries as it enables the creation of physiologically relevant platforms. A triple-flow microfluidic device is developed to rapidly fabricate alginate/graphene hollow microfibers based on the gelation of alginate induced with CaCl2 . This five-channel microdevice actualizes continuous mild fabrication of hollow fibers under an optimized flow rate ratio of 300:200:100 µL min-1 . The polymer solution is 2.5% alginate in 0.1% graphene and a 30% polyethylene glycol solution is used as the sheath and core solutions. The biocompatibility of these conductive microfibers by encapsulating mouse astrocyte cells (C8D1A) within the scaffolds is investigated. The cells can successfully survive both the manufacturing process and prolonged encapsulation for up to 8 days, where there is between 18-53% of live cells on both the alginate microfibers and alginate/graphene microfibers. These unique 3D hollow scaffolds can significantly enhance the available surface area for nutrient transport to the cells. In addition, these conductive hollow scaffolds illustrate unique advantages such as 0.728 cm3  gr-1 porosity and two times more electrical conductivity in comparison to alginate scaffolds. The results confirm the potential of these scaffolds as a microenvironment that supports cell growth.

Capacitance of Flexible Polymer/Graphene Microstructures with High Mechanical Strength

Carbon-modified fibrous structures with high biocompatibility have attracted much attention due to their low cost, sustainability, abundance, and excellent electrical properties. However, some carbon-based materials possess low specific capacitance and electrochemical performance, which pose significant challenges in developing electronic microdevices. In this study, we report a microfluidic-based technique of manufacturing alginate hollow microfibers incorporated by water dispersed modified graphene (bovine serum albumin-graphene). These architectures successfully exhibited enhanced conductivity ∼20 times higher than alginate hollow microfibers without any significant change in the inner dimension of the hollow region (220.0 ± 10.0 μm) compared with pure alginate hollow microfibers. In the presence of graphene, higher specific surface permeability, active ion adsorption sites, and shorter pathways were created. These continuous ion transport networks resulted in improved electrochemical performance. The desired electrochemical properties of the microfibers make alginate/graphene hollow fibers an excellent choice for further use in the development of flexible capacitors with the potential to be used in smart health electronics.

Electrospinning and Cell Fibers in Biomedical Applications

Human body tissues such as muscle, blood vessels, tendon/ligaments, and nerves have fiber-like fascicle morphologies, where ordered organization of cells and extracellular matrix (ECM) within the bundles in specific 3D manners orchestrates cells and ECM to provide tissue functions. Through engineering cell fibers (which are fibers containing living cells) as living building blocks with the help of emerging "bottom-up" biomanufacturing technologies, it is now possible to reconstitute/recreate the fiber-like fascicle morphologies and their spatiotemporally specific cell-cell/cell-ECM interactions in vitro, thereby enabling the modeling, therapy, or repair of these fibrous tissues. In this article, a concise review is provided of the "bottom-up" biomanufacturing technologies and materials usable for fabricating cell fibers, with an emphasis on electrospinning that can effectively and efficiently produce thin cell fibers and with properly designed processes, 3D cell-laden structures that mimic those of native fibrous tissues. The importance and applications of cell fibers as models, therapeutic platforms, or analogs/replacements for tissues for areas such as drug testing, cell therapy, and tissue engineering are highlighted. Challenges, in terms of biomimicry of high-order hierarchical structures and complex dynamic cellular microenvironments of native tissues, as well as opportunities for cell fibers in a myriad of biomedical applications, are discussed.

Alginate-based materials for enzyme encapsulation

Enzymes are widely used in industry due to their high efficiency and selectivity. However, their low stability during certain industrial processes can result in a significant loss of catalytic activity. Encapsulation is a promising technique that can stabilize enzymes by protecting them from environmental stresses such as extreme temperature and pH, mechanical force, organic solvents, and proteases. Alginate and alginate-based materials have emerged as effective carriers for enzyme encapsulation due to their biocompatibility, biodegradability, and ability to form gel beads through ionic gelation. This review presents various alginate-based encapsulation systems for enzyme stabilization and explores their applications in different industries. We discuss the preparation methods of alginate encapsulated enzymes and analyze the release mechanisms of enzymes from alginate materials. Additionally, we summarize the characterization techniques used for enzyme-alginate composites. This review provides insights into the use of alginate encapsulation as a means of stabilizing enzymes and highlights the potential benefits for various industrial applications.

Microfluidic Seeding of Cells on the Inner Surface of Alginate Hollow Microfibers

Mimicking microvascular tissue microenvironment in vitro calls for a cytocompatible technique of manufacturing biocompatible hollow microfibers suitable for cell-encapsulation/seeding in and around them. The techniques reported to date either have a limit on the microfiber dimensions or undergo a complex manufacturing process. Here, a microfluidic-based method for cell seeding inside alginate hollow microfibers is designed whereby mouse astrocytes (C8-D1A) are passively seeded on the inner surface of these hollow microfibers. Collagen I and poly-d-lysine, as cell attachment additives, are tested to assess cell adhesion and viability; the results are compared with nonadditive-based hollow microfibers (BARE). The BARE furnishes better cell attachment and higher cell viability immediately after manufacturing, and an increasing trend in the cell viability is observed between Day 0 and Day 2. Swelling analysis using percentage initial weight and width is performed on BARE microfibers furnishing a maximum of 124.1% and 106.1%, respectively. Degradation analysis using weight observed a 62% loss after 3 days, with 46% occurring in the first 12 h. In the frequency sweep test performed, the storage modulus (G') remains comparatively higher than the loss modulus (G″) in the frequency range 0-20 Hz, indicating high elastic behavior of the hollow microfibers.

Graphene Microelectrodes for Real-Time Impedance Spectroscopy of Neural Cells

Understanding the changes in the electrochemical properties of neural cells upon exposure to stress factors imparts vital information about the conditions prior to their death. This study presents a graphene-based biosensor for real-time monitoring of N27 rat dopaminergic neural cells which characterizes cell adhesion and cytotoxicity factors through impedance spectroscopy. The aim was to monitor the growth of the entire cell network via a nonmetallic flexible electrode array. Therefore, a water-based graphene solution was formulized as a conductive ink, 3D-printed into a flexible substrate through an electrohydrodynamic approach, resulting in electrodes with a conductivity of 6750 s/m. The presented high-throughput method enabled microscale monitoring of the entire cell network via the design of PDMS-based growth channels. The electrical resistance of the cell network was measured continuously along with their network density, constituting a mean density of 1890 cell/mm² at full cell confluency. The results demonstrate the applicability of the impedance-based sensing of the cell network for rapid screening of the cytotoxic elements, and the real-time effect of UV exposure on dopaminergic neural cells was reported as an immediate application of the device.